The present invention relates to an outer rotor type magneto generator including a magnet rotor comprised by mounting a permanent magnet to an inner periphery of a peripheral wall of a substantially cup-shaped rotor yoke, and an armature placed inside the magnet rotor.
An outer rotor type magneto generator includes, as shown in FIGS. 6A and 6B, a magnet rotor 3 having a rotor yoke 1 formed to become a substantial cup shape having a peripheral wall 1a and a bottom wall 1b, and a permanent magnet 2 mounted to an inner periphery of the peripheral wall 1a of the rotor yoke 1, and an armature 4 placed inside the magnet rotor 3.
The rotor yoke 1 has a boss 1c at the center of the bottom wall 1b, and the boss is mounted to a rotation axis of an unshown prime mover (in many cases, an internal combustion engine).
The armature 4 includes an armature core 5 and an armature coil 6 wound around the armature core, and is secured to a casing or the like of the prime mover, so that a magnetic pole portion provided on an outer peripheral portion of the armature core 5 faces the magnet 2 of the magnet rotor 3 with a predetermined gap therebetween. A generator shown in FIGS. 6A to 6C is disclosed in Japanese Patent Publication No.6-91718.
In such a generator, the armature coil 6 is heated by the loss produced when a load current passes through the armature coil 6, and in order to produce large output from the generator, efficient cooling of the armature coil is required.
Japanese Patent Publication No. 6-91718 proposes a cooling structure where a bottom wall 1b of a rotor yoke 1 is drilled to form a plurality of air vents 1d, 1d, . . . along an outer peripheral portion of the bottom wall 1b, and a cooling air introducing portion 9xe2x80x2 corresponding to each air vent 1d is provided in an annular plate 8 secured by screws 7 to an outer surface of the bottom wall 1b of the rotor yoke 1, thereby introducing cooling air into each air vent 1d through a cooling air introducing passage 10xe2x80x2 inside the cooling air introducing portion 9xe2x80x2.
As shown in FIG. 6C, the cooling air introducing portion 9xe2x80x2 is formed to protrude in an opposite direction to the bottom wall 1b and cover at least a part of a corresponding air vent 1d, and the cooling air introducing passage 10xe2x80x2 having a semicircular section is formed inside the cooling air introducing portion 9xe2x80x2. The cooling air introducing passage 10xe2x80x2 is provided to open forward in the rotational direction of the rotor yoke 1 (in the direction of the arrow in FIG. 6A).
In the magneto generator disclosed in Japanese Patent Publication No. 6-91718, as shown in FIG. 6A, the cooling air introducing portion 9xe2x80x2 is provided so that the cooling air introducing passage 10xe2x80x2 opens tangentially of the outer peripheral portion of the rotor yoke. This, combined with the semicircular section of the cooling air introducing passage 10xe2x80x2, prevents increase in sectional area of an opening of the cooling air introducing passage 10xe2x80x2. Thus, the amount of cooling air blown on the armature 4 through the air vent 1d is limited, which prevents enhancement of the cooling effect of the armature.
An object of the present invention is to provide a magneto generator capable of blowing cooling air larger in amount than a conventional magneto generator on an armature through an air vent provided in a bottom wall of a rotor yoke to enhance the cooling effect of the armature.
The invention is directed to a magneto generator including: a magnet rotor having a cup-shaped rotor yoke with a peripheral wall and a bottom wall, and a permanent magnet mounted to an inner periphery of the peripheral wall of the rotor yoke; and an armature placed inside the magnet rotor.
In the invention, the bottom wall of the rotor yoke is drilled at a portion closer to an outer periphery to circumferentially provide a plurality of air vents in the peripheral wall of the rotor yoke, and a hollow cooling air introducing portion is provided for each of the plurality of air vents.
Each cooling air introducing portion is provided to protrude in an opposite direction to an opening in the peripheral wall of the rotor yoke and cover at least a part of a corresponding air vent, and a cooling air introducing passage is formed inside the cooling air introducing portion.
An end of the cooling air introducing passage inside the cooling air introducing portion communicates with the inside of the rotor yoke through a corresponding air vent, while the other end of the cooling air introducing passage inside the cooling air introducing portion opens forward in the rotational direction of the magnet rotor through an opening end provided in the cooling air introducing portion.
The cooling air introducing portion has an outer side wall provided to extend in a sloping direction from near a corresponding air vent toward an outer peripheral portion of the rotor yoke and reach the opening end of the cooling air introducing portion.
The opening end of the cooling air introducing portion is directed in a sloping direction toward an inner diameter of the rotor yoke with respect to the direction orthogonal to a reference plane including both a straight line between the center of the bottom wall of the rotor yoke and the center of a corresponding air vent, and a central axis of the rotor yoke.
As described above, the outer side wall of the cooling air introducing portion is provided to extend in the sloping direction from near the corresponding air vent toward the outer peripheral portion of the rotor yoke and reach the opening end of the cooling air introducing portion, and the opening end of the cooling air introducing portion is directed in the sloping direction with respect to the direction orthogonal to the reference plane. This allows a sectional area of the cooling air introducing passage at the opening end of the cooling air introducing portion to be larger than a sectional area of the cooling air introducing passage inside a portion along the reference plane of the cooling air introducing portion.
Therefore, according to the invention, the cooling air introducing passage has a larger opening area than a conventional magneto generator having the opening end of the cooling air introducing portion opening tangentially of the rotor yoke, and thus a larger amount of cooling air can be introduced into the cooling air introducing portion with rotation of the rotor to enhance the cooling effect of the armature as compared with the conventional magneto generator of this type.